Life of a transition director

Discussion thread	Status
	Drafting as of Oct 25, 2016

Let's walk through the life of a simple fade transition director.

Remember, any code you see here is pseudo-code.

Step 1: Define a new TransitionDirector type

This object conforms to the TransitionDirector type.

TransitionDirector FadeTransitionDirector {
  let transition: Transition
  init(transition: Transition) {
    self.transition = transition
  }
}

Step 2: Implement the setUp method

Our setUp might use a simple Tween plan:

class FadeTransitionDirector: TransitionDirector {
  function setUp() {
    var tween = Tween(.opacity, duration: transition.duration)
    if initialDirection == .forward {
      tween.from = 0
      tween.to = 1
    } else {
      tween.from = 1
      tween.to = 0
    }
    transition.addPlan(tween, to: transition.fore)
  }
}

Or TweenBetween to reduce the need for conditional logic:

class FadeTransitionDirector: TransitionDirector {
  function setUp() {
    var tween = TweenBetween(.opacity,
                             window: transition.window,
                             segment: transition.entire,
                             back: 0,
                             fore: 1)
    transition.addPlan(tween, to: transition.fore)
  }
}

Step 3: Associate the director with a transition controller

This step is platform-specific.

iOS

To configure the present/dismiss transition for a view controller, set the Director on the view controller's transitionController:

viewController.mdm_transitionController.directorType = typeof(FadeTransitionDirector)

Step 4: Initiate the transition

Initiating our transition causes FadeTransitionDirector to be instantiated and its setUp method is invoked. The plans expressed by the director will then be executed.

Upon completion, the director instance is thrown away.